France's Vinci SA (DG.FR) said Tuesday that the Nanterre public prosecutor's office has dropped an investigation into working conditions for employees in Qatar.

The investigation was opened in 2015 after Paris-based association Sherpa filed a complaint against Vinci and its Qatari subsidiary, alleging the companies' treatment of migrant workers violated international laws.

Sherpa said it will take further action and file another complaint.

The group's aim is to defend victims of economic crime, according to its website.

Vinci has always disputed the claims and filed a defamation suit against Sherpa, which was subsequently rejected in July 2017.

"As Vinci has stated all along, it endeavors not only to observe local employment law and fundamental rights, but also to make constant improvements to the working and living conditions of its employees," the company said in a release.